1. Field of the Invention
The present invention relates to a liquid crystal projector.
2. Description of the Prior Art
In liquid crystal projectors, a liquid crystal panel, a light source lamp for backlight arranged on a rear surface of the liquid crystal panel, a signal processing circuit, and a power supply circuit are provided in a casing. Cooling fans for cooling the liquid crystal panel, the light source lamp for backlight, and so on are provided in the casing of the liquid crystal projector. Conventionally, the higher the number of revolutions of the cooling fan is, the more the cooling efficiency is improved. However, noise is increased.
In a case where the internal temperature of the liquid crystal projector is detected, to determine a control voltage for the cooling fan in proportion to the detected temperature, when only one temperature sensor is employed, and a driving voltage for the cooling fan is controlled on the basis of the temperature detected by the temperature sensor, the internal temperature of the liquid crystal projector is determined depending on the position where the one temperature sensor is mounted.
Inside the liquid crystal projector, it is considered that there occurs a temperature difference in its inner place depending on various factors, for example, the temperature of the outside air and judgment whether or not there is a sufficient space in the vicinity of a vent hole. When the temperature partially rises inside the liquid crystal projector, the partial rise in the temperature cannot, in some cases, be detected depending on the position where the temperature sensor is mounted.
An object of the present invention is to provide a liquid crystal projector capable of detecting, when the temperature partially rises inside a liquid crystal projector, the partial rise in the temperature and controlling a driving voltage for a cooling fan.
In a liquid crystal projector provided with a cooling fan, a first liquid crystal projector according to the present invention is characterized by comprising a plurality of temperature sensors for detecting the internal temperature of the liquid crystal projector and a fan control circuit for controlling a driving voltage for the cooling fan on the basis of a temperature detected by each of the temperature sensors, the fan control circuit comprising means for calculating, on the basis of the temperature detected by each of the temperature sensors and a temperature range determined depending on the position where the temperature sensor is mounted, the ratio of the detected temperature to the temperature range for the temperature sensor, and means for controlling the driving voltage for the cooling fan on the basis of the maximum of the ratio of the detected temperature to the temperature range which has been calculated for each of the temperature sensors.
In a liquid crystal projector provided with a cooling fan, a second liquid crystal projector according to the present invention is characterized by comprising a plurality of temperature sensors for detecting the internal temperature of the liquid crystal projector and a fan control circuit for controlling a driving voltage for the cooling fan on the basis of a temperature detected by each of the temperature sensors, the fan control circuit comprising a circuit for calculating, on the basis of the temperature detected by each of the temperature sensors and a temperature range determined depending on the position where the temperature sensor is mounted, the ratio of the detected temperature to the temperature range for the temperature sensor, and a circuit for controlling the driving voltage for the cooling fan on the basis of the maximum of the ratio of the detected temperature to the temperature range which has been calculated for each of the temperature sensors.
When there are two temperature sensors, one of the temperature sensors is arranged in the vicinity of a light source lamp for backlight, for example, and the other temperature sensor is arranged at the position where the temperature thereof is close to the temperature of the outside air, for example.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.